The air-to-fuel ratio (A/F) referred in the present invention refers to the volumetric ratio of the air to fuel in the exhaust gas from an engine. To attain an ideal operating condition for an engine, the air-to-fuel ratio of the air-fuel mixture is controlled around 14.7, as shown by the shadowed region in FIG. 1. This region not only avoids incomplete combustion of the fuel but also enhances cleaning pernicious gases in the exhaust gas by reduction and oxidation reactions.
The motorcycles in the market do not have an air-to-fuel ratio control means, except for those equipped with an engine control unit (ECU) and oxygen sensor. Considering production cost, motorcycles with small values of air displacement do not have an oxygen sensor. Without an oxygen sensor, precise control of the air-to-fuel ratio near 14.7 is difficult so that the combustion efficiency of the engine is low and the problem of incomplete combustion becomes more significant.
Further, the factors influence the effectiveness of inverting exhaust gas from a motorcycle engine include the technology of installing catalysts and the arrangement of a secondary air inlet. A common method of the prior art is installing one or more than one metallic catalyst carriers doped with precious metals selected from rhodium (Rh), platinum (Pt) and palladium (Pd) in the exhaust pipe of a motorcycle. A secondary air inlet is further installed in front of the catalyst carriers for sucking the air from outside into the exhaust pipe so that the air-to-fuel ratio of the exhaust gas becomes larger than 14.7, enhancing the efficiency of inverting carbon monoxide (CO) and hydrocarbons (HC) effectively into carbon dioxide (CO2) and water (H2O). However, the high oxygen content of the exhaust gas and the high temperature due to oxidation seriously lower the efficiency of inverting nitrogen oxides (NOX). And the nitrogen oxides (NOX) therefore released in the atmosphere contribute to the formation of acid rains and the destruction of the ozone layer.
There are some prior arts related to the present invention. One of the prior art is U.S. Pat. No. 3,943,709, in the prior art, process and apparatus for reducing emissions from internal combustion engine exhaust gas. The exhaust gas treatment system includes a first stage converter containing a NO.sub.x reduction catalyst, a second stage converter containing a catalyst for oxidation of CO and hydrocarbons, and means for admitting secondary air to the inlet of the second stage. Reduced CO and hydrocarbon emissions are obtained by admitting air in an amount not greater than that required to achieve a stoichiometric mixture to the inlet of the first stage during cold (i.e., choked) engine operation, discontinuing the flow of air to the first stage inlet when the average air-fuel ratio reaches approximately its normal warm engine value, and thereafter continuing operation without adding an appreciable quantity of air to the inlet of the first stage. The engine is operated with a substantially net rich average air-fuel ratio during warmup and with a slightly net rich average air-fuel ratio thereafter.
In another prior art, U.S. Pat. No. 5,706,653, a secondary air supply apparatus for an internal combustion engine is provided with an air-fuel ratio sensor disposed upstream of an catalytic converter in an exhaust passage. An outlet port of a secondary air supply conduit is formed upstream of and in the vicinity of the air-fuel ratio sensor. Air discharged from an air pump is supplied to the exhaust passage through the secondary air supply conduit. A control unit diagnoses as to whether or not the air-fuel ratio sensor is activated by checking as to whether a detection signal of the air-fuel ratio sensor is out of a predetermined range or not. Then, the control unit diagnoses as to whether the supply of the secondary air is normal or not on the basis of the detection signal of the air-fuel ratio sensor. Therefore, the diagnosis of the supply of the secondary air is correctly executed.
In another prior art U.S. Pat. No. 3,896,616 discloses an exhaust gases from internal combination engine which are purified by catalyst treatment. The systems have an initial catalyst, preferable in a separate vessel near the engine, and a substantially-in-line catalyst. Preferably, the catalysts are of the honey-type. The exhaust gases and an excess of oxygen, with or without a supplemental fuel, are passed through the initial catalyst during the start up of the engine to insure that the exhaust gases are purified more or less as soon as the engine begins operation. In order to reduce the amount of nitrogen oxides in the exhaust after start-up an excess of extraneous fuel is fed to the initial catalyst to reduce nitrogen oxides to nitrogen. The subsequently in line catalyst serves to reduce the carbon monoxide and hydrocarbon contents of the exhaust gases.
Above three citations provide an exhausting gas purifying system, which conclude reduction catalyst and oxidation catalyst so as to purifying the wasted gas from an engine. However as we know above mentioned structure can not effective purifying the exhausting gas. There is an eager demand for a novel design which can effectively purifying waste gas.
The division of the muffler into the first, second and third chambers has the effect of disturbing the molecules in the gas so as to clean the exhausting gas from the outlet of the rear exhaust pipe. Thus the exhaust gas is processed effectively.